Functional characterisation of stress granule composition and morphology

Effective cellular stress response programs minimize damage and allow cells to survive unfavourable conditions. In eukaryotic cells, many stresses (e.g. heat shock, ultraviolet (UV) light damage, oxidative stress) cause transient cessation of protein synthesis to decrease energy consumption and facilitate reprogramming of gene expression. This translation arrest results in formation of stress granules (SGs) cytoplasmic foci that contain untranslated messenger ribonucleoproteins (mRNPs). These foci form because polysome-free mRNPs recruit proteins with self-aggregating properties, such as the T-cell intracellular antigen 1 (TIA1) and the Ras GTP-ase activating protein binding proteins 1 and 2 (G3BP1/2) that nucleate SG formation. SG formation has been demonstrated for eukaryotes from yeast to humans and thus represents an evolutionarily conserved stress response pathway. However, the functional significance of mRNP aggregation into SGs and its role in responses to different types of stress remain unknown and will represent the long-term objective of my NSERC-funded research program. It is well established that SG formation is not required for stress-induced translation arrest. Thus, other functions have been suggested for SGs, including a) storage and triage of untranslated mRNAs; b) regulation of signaling cascades during stress; c) disruption of nucleocytoplasmic transport through sequestration of specific factors. Even if these and possibly additional functions could be attributed to SGs, their role in response to different types of stress have not been demonstrated to date. Accordingly, elucidating the functions of SGs in various stress response pathways will be one of the major research objectives in my laboratory. In the short term, I will focus on UV light-induced SG formation and the role of SGs in cell survival following UV damage (Aim 1). In parallel, I will characterize stress-dependent differences in SG composition using a proximity proteomics approach (Aim 2).

Proposed studies will answer several important questions relating to SG biology: a) how signaling cascades activated by UV light dictate unique composition and properties of SGs formed following UV exposure; b) how SG formation affects cell survival following UV damage; c) the extent of stress-specific differences in SG composition. The answers to these questions will contribute new knowledge to the field of RNA granule biology that is steadily growing and will inform future studies into functional consequences of SG formation in response to different stress conditions.